Professor Randall Feenstra
Professor, Physics
Ph.D., California Institute of Technology

6408 Wean Hall
Carnegie Mellon University
Pittsburgh, PA 15213-3890

Email address: 
Phone: (412) 268-6961
Fax: (412) 681-0648

Professor Feenstra's Web Site

The research activities of my group deal with structural and electronic properties of semiconductor materials and devices. The major tool used in the studies is the scanning tunneling microscope, which allows one to image the atomic structure of a surface and to perform spectroscopic measurements of the electronic energy levels. Studies performed in the past include atom specific imaging of different chemical species on a surface, and observations of atomic diffusion leading to surface phase transitions at elevated temperature. More recently, we have studied semiconductor heterostructures consisting of multiple layers of different types of material, with the goal of understanding how the structure of the device (including imperfections and defects) determines its electronic properties.

Growth of semiconductor heterostructures is performed in my laboratory using molecular beam epitaxy. We have concentrated on the growth of GaN, a semiconductor with a relatively large band gap used for blue light-emitting devices and for microwave transistor applications. Our focus is surface studies of the GaN films. From studies of the surface reconstructions we have deduced mechanisms for film growth and for incorporation of various species such as In, Si, and Mg used in doping and alloy formation.

C. D. Lee, Ashutosh Sagar, R. M. Feenstra, C. K. Inoki, T. S. Kuan, W. L. Sarney and L. Salamanca-Riba, "Role of Ga-flux in dislocation reduction in GaN films grown on SiC(0001)", Appl. Phys. Lett. 79, 3428 (2001).

R. M. Feenstra, G. Meyer, F. Moresco, and K. H. Rieder, "Buckling and band gap of the Ge(111)2x1 surface studied by low-temperature scanning tunneling microscopy". Phys. Rev. B 64, 081306(R) (2001).

H. A. McKay, R. M. Feenstra, T. Schmidtling and U. W. Pohl, "Arrangement of Nitrogen Atoms in GaAsN Alloys determined by Scanning Tunneling Microscopy". Appl. Phys. Lett. 78, 82 (2001).

H. Chen, R. M. Feenstra, J. E. Northrup, T. Zywietz,and J. Neugebauer, "Spontaneous Formation of Indium-rich Nanostructures on InGaN(0001) Surfaces", Phys. Rev. Lett. 85, 1902 (2000).

H. Chen, R. M. Feenstra, J. E. Northrup, T. Zywietz, J. Neugebauer, and D. W. Greve, J. Vac, "Surface structures and growth kinetics of InGaN(0001) grown by molecular beam epitaxy", Sci. Technol. B 18, 2284 (2000).

W. L. Sarney, L. Salamanca-Riba, V. Ramachandran, R. M. Feenstra, and D. W. Greve, "TEM Study of the Morphology Of GaN/SiC (0001) Grown at Various Temperatures by MBE", MRS Internet J. Nitride Semicond. Res. 5S1, W3.47 (2000).

V. Ramachandran, R. M. Feenstra, J. E. Northrup, and D. W. Greve, "Surface activity of magnesium during GaN molecular beam epitaxial growth", MRS Internet J. Nitride Semicond. Res. 5S1, W3.65 (2000).

V. Ramachandran, R. M. Feenstra, W. L. Sarney, L. Salamanca-Riba, and D. W. Greve, J. Vac, "Optimized structural properties of wurtzite GaN on SiC(0001) grown by molecular beam epitaxy", Sci. Technol. A 18, 1915 (2000).

R. M. Feenstra, H. Chen, V. Ramachandran, A. R. Smith, D. W. Greve, "Reconstructions of GaN and InGaN Surfaces", Appl. Surf. Sci. 166, 165 (2000).

V. Ramachandran, C. D. Lee, R. M. Feenstra, A. R. Smith, J. E. Northrup, and D. W. Greve, J., "Structure of Clean and Arsenic-covered GaN(0001) Surfaces", Cryst. Growth 209, 355 (2000).

V. Ramachandran, R. M. Feenstra, W. L. Sarney, L. Salamanca-Riba, J. E. Northrup, L. T. Romano, and D. W. Greve, "Inversion of wurtzite GaN(0001) by exposure to magnesium", Appl. Phys. Lett. 75, 808 (1999).

R. M. Feenstra, "Tunneling spectroscopy of the Si(111)2x1 surface", Phys. Rev. B 60, 4478 (1999).